Patients treated with BCT have historically received radiation to the entire breast followed by a boost to the tumor bed. This boost may be delivered using photons, electrons, or radioactive implant.

Recently, several centers have initiated use of techniques delivering radiotherapy only to the tumor bed after lumpectomy, rather than the whole breast; this method of treatment is globally referred to as partial breast irradiation (PBI).

The MammoSite® Radiation Therapy System (RTS) has been developed in efforts to deliver radiotherapeutic dose to tumor bed and the region surrounding it.

Patients undergoing treatment with MammoSite® RTS undergo placement of the MammoSite® balloon into the lumpectomy cavity at the time of lumpectomy.

Following this, high-dose rate brachytherapy is delivered via the balloon to the lumpectomy category twice daily, over 5 days.

After radiotherapy is completed, the MammoSite® balloon is removed.

The Mammosite® RTS was FDA approved for treatment of early-stage breast cancer in May, 2002. At that time, the Mammosite® RTS Registry Trial was begun; its control was assumed by the American Society of Breast Surgeons (ASBS) in November, 2002.

Recommended patient eligibility requirements include age of at least 45 years, small tumor size, negative surgical margins, and a distance of at least 7 mm from the lumpectomy cavity to the skin surface.

Over the 6 years during which Mammosite® RTS technology has been employed, several centers have reported local recurrence rates and overall survival; however, to date, these trials have analyzed small numbers of patients at single institutions.

Patients were enrolled on the registry from 97 different institutions, and received care from 121 different physicians.

A total of 1440 women were treated with Mammosite® RTS technology from May, 2002 until September, 2004. Among these women, 9 had bilateral tumors both treated with Mammosite® RTS. A total of 1449 tumors were thus analyzed.

The authors conclude that PBI with Mammosite® RTS results in low rates of IBTR and axillary recurrence, and acceptable cancer specific survival.

They note that the first 400 consecutive cases, with 5 years of follow-up, had equivalent recurrence rates as the group as a whole.

They describe similar associations with increased risk of IBRT, such as extensive intraductal component, non-use of Tamoxifen, and high histologic grade as have been noted in previous studies.

Clinical/Scientific Implications

The Mammosite® RTS and PBI in general have gained popularity among clinicians and patients over the recent decade.

As the authors point out, most reports have included relatively small numbers of patients, and this study represents an important contribution to the literature.

With 5 years of follow-up, local recurrence and overall survival rates appear to be acceptable and equivalent to those documented for traditional, whole breast radiotherapy with boost after lumpectomy (Santiago RJ, IJROBP, 2006).

The importance of considerably longer follow-up should not be undervalued, however. Large studies have demonstrated that patients treated for early-stage breast cancer remain at risk for recurrent disease for at least 15 years after having completed treatment (Santiago RJ, IJROBP, 2006). This risk appears to be relatively constant.

Additionally, the authors do not comment on cosmetic outcome following treatment with Mammosite® RTS. Certainly, the use of implant-based radiotherapy raises questions regarding cosmetic outcome when compared to external beam radiotherapy, and these questions are largely unanswered. In addition, the delivery of an accelerated schedule of radiation to only a small part of the breast raises concern for breast asymmetry resulting years after treatment. Analysis of cosmetic outcome would be interesting at this point, and potentially more interesting with increased follow-up.

This study has relatively short follow-up compared to the breast literature as a whole; however, it represents one of the first large analyses of PBI delivered with the Mammosite® RTS. This system is employed to treat a large number of patients after lumpectomy with early stage breast cancer, and this trial is certainly an important contribution to their care. As follow-up time increases, future studies will offer long-term perspective on both cancer outcomes and cosmetic results for patients who choose this method of treatment.

May 7, 2012 - Men with breast cancer are more likely to present with larger tumors of higher grade which have metastasized, and they have worse five-year overall survival than women for earlier stages of the disease, according to a study presented at the annual meeting of the American Society of Breast Surgeons, held from May 2 to 6 in Phoenix.